This invention relates to an assembly and method for delivering and deploying an expandable stent, particularly within a lumen of a body vessel. More specifically, this invention relates an assembly and method for delivering and deploying a balloon expandable stent, and most notably to stent securement devices positioned over the balloon and stent.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well-known. A stent is a general cylindrical prosthesis introduced via a catheter into a lumen of a body vessel, the stent being in a configuration having a generally reduced diameter and then being expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation (as by a balloon) expandable stents are well-known and widely available. Self-expanding stents must be maintained under positive external pressure in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents (also known as balloon expandable stents) are generally crimped to their reduced diameter about the delivery catheter, positioned at the deployment site, and then expanded to the vessel diameter by fluid inflation of the balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with stent securement in the delivery and deployment of inflation expandable stents.
In angioplasty procedure, there may be restenosis of the artery, which either necessitates another angioplasty procedure, a surgical bypass procedure, or some method of repairing or strengthening the area. To prevent restenosis and strengthen the area, a physician may implant an intravascular prosthesis for maintaining vascular patency, i.e. a stent, inside the artery at the lesion. The stent is expanded to a larger diameter following placement in the vasculature, often by a balloon portion of the catheter. Stents delivered to a restricted coronary artery, expanded to a larger diameter as by a balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer; U.S. Pat. No. 5,007,926 to Derbyshire; U.S. Pat. No. 4,733,665 to Palmaz; U.S. Pat. No. 5,026,377 to Burton et al.; U.S. Pat. No. 5,158,548 to Lau et al.; U.S. Pat. No. 5,242,399 to Lau et al.; U.S. Pat. No. 5,344,426 to Lau et al.; U.S. Pat. No. 5,415,664 to Pinchuck; U.S. Pat. No. 5,453,090 to Martinez et al.; U.S. Pat. No. 4,950,227 to Savin; U.S. Pat. No. 5,403,341 to Solar; U.S. Pat. No. 5,108,416 to Ryan et al.; and European Patent Application No. 707837A1 to Scheiban, all of which are incorporated herein by reference. A stent particularly preferred for use with this invention is described in PCT Application No. 96/03092-A1, published Feb. 8, 1996, the content of which is also incorporated herein by reference.
In advancing a inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter. The stent, particularly its distal and proximal ends, are sometimes protected to prevent distortion of the stent, and minimize trauma to the vessel walls. Balloon expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to a balloon expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of a stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s) and the sleeve(s) then collapse upon the delivery catheter for removal. U.S. Pat. No. 5,403,341 to Solar, relates to stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent for engagement with the implant site. U.S. Pat. No. 5,108,416 to Ryan et al. describes a stent introducer system which uses one or two flexible end caps and annular socket surrounding the balloon to position the stent during introduction to the deployment site. The content of all of these patents is incorporated herein by reference.
In positioning a balloon expandable stent on a delivery catheter over a fluid expandable balloon, the stent is preferably smoothly and evenly crimped to closely conform to the overall profile of the catheter and the unexpanded balloon. It has been noted that, due to physical properties of the material used in manufacturing stents (typically stainless steel or a shape memory metal, such as Nitinol(trademark)) there is a certain amount of xe2x80x9crecoilxe2x80x9d of the stent despite the most careful and firm crimping. That is the stent evidences a tendency to slightly open up from the fully crimped position once the crimping force has been released. For example, in a typical stainless steel stent delivery and deployment assembly, if the stent has been fully crimped to a diameter of approximately 0.0035xe2x80x3, such stents have been observed to open up or recoil to approximately 0.0037xe2x80x3 in diameter. This phenomenon has been characterized as xe2x80x9crecoil crimpingxe2x80x9d. Due to recoil crimping to this slightly enlarged diameter, it can be understood that stents in such instances may tend to evidence a certain amount of looseness from their desired close adherence to the overall profile of the underlying catheter and balloon. That is, such stents may tend to have a perceptible relatively slack fit in their mounted and crimped position. During delivery, such a stent may thus tend to slip or dislocate from a desired position on the catheter or even become separated from the catheter, requiring further intervention by the physician.
One important characteristic of a balloon catheter is its xe2x80x9cprofilexe2x80x9d, which is determined by the outer diameter (O.D.) of the distal end portion of the catheter, which includes a balloon and stent when the combination is in its delivery profile. The outer diameter affects the ease and ability of the catheter to pass through a guide catheter, through coronary arteries for example, and across a tight lesion site. Considerable effort has been made in developing low profile balloon catheters. U.S. Pat. No. 5,342,307, incorporated herein by reference, discloses a balloon protector sleeve used with a tri-fold balloon catheter for angioplasty. Minimization of xe2x80x9cprofilexe2x80x9d is of importance in balloon catheters and stent delivery systems.
The present invention is particularly directed to improved arrangements to secure and cover a stent on a delivery catheter to better facilitate delivery thereof. The securement devices secure the stent to the catheter during tracking and delivery. The present invention also provides an improved arrangement of a stent delivery system with a minimized profile.
The stent securement device of the present invention is of particular utility with such stent delivery systems as are set forth in U.S. Pat. Nos. 5,571,168 and 5,733,267 for PULL BACK STENT DELIVERY SYSTEM, U.S. application Ser. No. 09/052,488 filed Mar. 31, 1998, U.S. application Ser. No. 08/807,791 filed Feb. 28, 1997, U.S. application Ser. No. 08/702,150 filed Aug. 23, 1996, U.S. application Ser. No. 08/697,453 filed Aug. 23, 1996, U.S. application Ser. No. 08/701,979, filed Aug. 23, 1997, U.S. application Ser. No. 08/702,149 filed Aug. 23, 1996, International Application PCT/US97/14980, and International Application PCT/US97/14141, all of which are incorporated by reference in their entirety.